Partial combustion, also known as gasification, of a solid carbonaceous fuel is obtained by the reaction of the fuel with oxygen. The fuel mainly contains carbon and hydrogen as combustible components. The gas-carried finely divided carbonaceous fuel and the oxygen-containing gas are passed via the separate channels in the burner into a reactor at relatively high velocity. In the reactor a flame is maintained in which the fuel reacts with the oxygen in the oxygen-containing gas at temperatures above 1300° C. to form mainly carbon monoxide and hydrogen.
The term “oxygen-containing gas” as used herein is intended to refer to gas containing free oxygen, O2, and to include air, oxygen-enriched air, i.e., more than 21 mole % oxygen, and also substantially pure oxygen, i.e., more than about 95 mole % oxygen, with the remainder comprising gases normally found in air such as nitrogen, and/or rare gases.
The term “solid carbonaceous fuel” as used herein is intended to include various gas carried combustible materials and mixtures thereof from the group of coal, coke from coal, coal liquefaction residues, petroleum coke, soot, biomass, and particulate solids derived from oil shale, tar sands and pitch. The coal may be of any type, including lignite, sub-bituminous, bituminous and anthracite. The solid carbonaceous fuels are preferably ground to a particle size so that at least about 90% by weight of the material is less than 90 microns and moisture content is less than about five percent weight.
U.S. Pat. No. 4,887,962 discloses a burner for such a partial combustion process. The burner comprises a central channel with an outlet for supplying the fuel to the combustion zone, and a coaxial annular channel with an outlet surrounding the central channel outlet to supply an oxygen containing gas intersecting and mixing with the flow of solid fuel from the outlet of the central channel. The burner further comprises a front face disposed at the discharge end of the burner. The front face has a central aperture through which the fuel and the oxygen containing gas flow to the combustion zone. Approaching the outlet, the diameter of the annular channel supplying the oxygen containing gas decreases resulting in an angle with respect to the longitudinal axis. The thus obtained inclining annular slit should be stably dimensioned in order to obtain a constant and evenly distributed flow of oxygen-containing gas. Due to the inclination of the annular slit in the flow direction, the issuing gas flow will intersect and mix with the flow of co-reactive combustible material issuing from the central channel into the downstream combustion zone.
Since the combustion temperatures may reach 1300° C. or more, a primary concern of such burners is to prevent damage to the burner front, also referred to as the burner face, caused by the high heat flux during the gasification process. To protect the burner front from overheating, U.S. Pat. No. 4,887,962 proposes to use a hollow wall member with internal cooling passages through which fluid coolant is circulated at a rapid rate along a spiral flow path to assure even cooling of the burner front face so as to minimize thermal stresses which could cause deterioration and even failure of the burner during prolonged operation, particularly by fatigue stresses, which may ultimately result in leaks of coolant. In U.S. Pat. No. 4,887,962 a large number of spiral turns is required to cool the complete burner front, resulting in considerable pressure drop.